Field experiments on stranding in juvenile atlantic salmon (Salmo salar) and brown trout (Salmo trutta) during rapid flow decreases caused by hydropeaking

Abstract

Field experiments showed that sudden reductions in river flow may cause high mortality of juvenile salmonids through stranding. A 75-m 2 enclosure in the drawdown zone of a regulated river was stocked with a known number of wild 0+ and/or 1+ wild Atlantic salmon (Salmo salar) and brown trout (Salmo trutta). The number stranded was estimated by counting the surviving fish collected in a bag as they left the enclosure.In general, a far higher incidence of fish stranding was found during winter conditions (B4.5°C) compared with the higher temperatures during late summer and early autumn. This is probably mainly because of lower fish activity during the cold season and a substrate seeking behaviour especially during daytime. Stranding was lower at night, probably because of a predominant night active behaviour. Hatchery salmon behaved oppositely to wild fish, and studies based on cultivated fish may give wrong conclusions as to the consequences of hydropeaking. Searching for fish in the substrate underestimated the consequences of sudden flow reductions, as fish were difficult to find. Stranding is not equal to mortality, as fish were found to survive for several hours in the substrate after dewatering. Long shut down procedures of the turbines during daytime, decreased stranding of Atlantic salmon (7 -9 cm) drastically under spring conditions. Temperature, season and light conditions have the most pronounced effect on stranding of juvenile salmonids. It is possible to reduce stranding by taking into account these ecological considerations during hydropeaking operations.

Hydropeaking indicators for characterization of the Upper-Rhone River in Switzerland

“…Juvenile fish are further endangered by drift and stranding in off-channel areas and exposed depositional features during water-level decreases (e.g. Baumann and Klaus 2003;Cushman 1985;Saltveit et al 2001). Stranding experiments with juvenile brown trout by Halleraker et al (2003) revealed a relationship between stranding and habitat quality, fish size, season, and ramping rates, as well as habituation to repeated dewatering.…”

A conservation plan for Atlantic salmon (Salmo salar) and anadromous brown trout (Salmo trutta) in a region with intensive industrial use of aquatic habitats, the Hardangerfjord, western Norway

“…In some large power plants, water from one drainage system is transferred to another, and in some the water from the power plant is released directly into the fjord with a reduction in available habitat as a consequence. In other regulated rivers, water is not transferred between drainages, but reduced discharges may have detrimental effects on salmonid production (Saltveit et al 2001;Johnsen et al 2011). Other effects on freshwater habitats include changes in water chemistry and temperature (Saltveit 1990), and channelization and draining of side-branches of rivers, which either reduce available habitat or make it otherwise less favourable.…”

Survival of eggs of Atlantic salmon (Salmo salar) in a drawdown zone of a regulated river influenced by groundwater

“…In regulated rivers groundwater influx may therefore create refuges for juveniles during low flows or 22 hydropeaking episodes (Saltveit et al, 2001). Eggs of fall-spawners may freeze during low flow periods in late 23…”